Gyro verticals serve the purpose of providing in a vehicle, for example a ship or an airplane, a reference direction, which is aligned with the true vertical and independent of pitch or roll movements of the vehicle and with respect to which such pitch or roll movements can be measured. Such a gyro vertical is used, for example, in an airplane as "artificial horizon." A gyro vertical comprises a gyro rotor rotating at high rotational speed in a gyro housing which is gimbal suspended within the vehicle. The gyro spin axis is aligned with the vertical. As the gyro tends to maintain its orientation in space this orientation is retained even if the vehicle makes pitch or roll movements.
Due to disturbing torques which, for example, are caused by friction in the gimbal bearings, the gyro has a drift, i.e. the gyro deviates slowly from the vertical direction, even if it had been aligned accurately therewith in the beginning. Therefore it is necessary to provide a device, which, at first, aligns the gyro spin axis with the vertical direction (erects it) and which then stabilizes this vertical direction against disturbing torques (stabilizes it).
To erect and stabilize a gyro vertical, it is known (U.S. Pat. No. 1,311,768) to arrange a disc on the gyro housing perpendicular to the gyro spin axis, said disc being driven in the same sense as the gyro rotor but with reduced rotational speed as compared thereto. In the prior art device, this disc has three arcuate guideways along its periphery, which are curved around the gyro spin axis and are angularly spaced by 120.degree.. A mass in the form of a ball is movably guided in each of these guideway portions and is supported on a raceway, which is located below the rotating disc and stationary with respect to the housing. When the disc rotates about an exactly vertical axis, the balls will abut the rear end, with respect to the rotary movement, of each arcuate guideway portion and will be taken along by the disc against the frictional forces acting on the balls. Thus in this state the balls are angularly spaced by 120.degree., and the disc with the balls is balanced with respect to the gyro spin axis. Therefore the disc does not exert any torque on the gyro. When, however, the gyro axis is tilted with respect to the vertical, the balls conveyed "uphill" during the revolution of the disc will be taken along by the rear ends of the arcuate guideway portions against the action of gravity and remain in abutment therewith, while the respective balls running "downhill" will leave the associated rear end of the guideway portion under the action of gravity, and thus will change its angular position with respect to the gyro spin axis. Then the disc with the balls is no longer balanced and exerts a torque on the gyro spin axis. This torque is directed to cause erection of the gyro spin axis.
Other designs described in U.S. Pat. No. 1,311,768 show other forms of guideways, balls which are arranged in a continuous circular guideway and are moved by radially projecting, rotating driving arms angularly spaced by 120.degree., and arrangements with masses with radial levers which are mounted for rotation about a central axis, said masses being taken along by axially projecting engaging pieces, which rotate relative to the gyro housing in the same sense as the gyro rotor. It has also been proposed already in U.S. Pat. No. 1,311,768 to use quantities of liquid instead of the balls.
The usual deviations of the gyro spin axis from the vertical direction, which are caused by disturbing torques, amount to few degress only. With heavy horizontal accelerations, for example during turns, there will be, however, larger deviations between the gyro spin axis and the apparent vertical occurring due to the acceleration. The gyro vertical has to be prevented from tending to align itself with the apparent vertical during such short-time acceleration phases. When a predetermined level of deviation of the gyro spin axis from the vertical is exceeded, this fact can be regarded as an indication that such a short time acceleration is acting on the system. During such acceleration phase the device for erecting the gyro vertical has to be disabled. Various designs for this purpose are known.
In a prior art device (German utility model No. 1,974,279), erection of the gyro vertical is caused by a ball which is movable in a guideway between stops. A counter-pendulum weight causes this movable ball to be arrested, as soon as the deviation of the gyro spin axis from the oberved vertical direction exceeds a predetermined level. Such designs with counter-pendulum weights for arresting masses are expensive and susceptible to trouble.
In the prior art designs the erecting torque is provided by displacing the masses only along an arc extending through a limited angle along the periphery of the disc.